This invention relates to a method of ion exchanging cations onto coal wherein the cations are one or more metals selected from the group consisting of alkali and alkaline-earth metals.
Although coal is by far our most abundant fossil fuel, there are serious problems associated with its use which has prevented it from reaching its full commercial potential. Examples of some such problems include problems in handling, waste-disposal, and pollution. There is also a need in the art for improved methods of pretreating coal to be used in combustion and in catalytic gasification processes. As a result of these problems and needs, oil and natural gas have acquired a dominant position, from the standpoint of fuel sources, throughout the world. This, of course, has led to depletion of proven petroleum and natural gas reserves to an alarming level from both a worldwide energy, as well as an economic point of view.
It is often desirable to have organically bound cations, such as calcium, atomically dispersed throughout the coal structure. These cations can be either naturally occurring or they may be introduced into the coal structure by ion-exchange techniques. Cations such as calcium, which are orgnically bound to the coal structure, are superior to admixtures of coal and inorganic calcium salts, such as limestone, for catalytic reasons, as well as for capturing sulfur in the resulting solid effluent.
Various conventional methods are known for organically incorporating cations into coal structures. For example, U.S. Pat. No. 4,092,125 teaches a hydrothermal method for organically binding, as well as physically incorporating, alkali and alkaline-earth metal ions into the coal structure. The method taught therein comprises mixing fine particles of solid carbonaceous fuel, such as coal, with a liquid solution comprising essentially a hydroxide of sodium, potassium, or lithium and a hydroxide or carbonate of calcium, magnesium, or barium. The mixture is then reacted in a closed reactor from a temperature of about 150.degree. C. to 375.degree. C.
Another conventional method is the method disclosed in U.S. Pat. No. 4,204,843 wherein calcium ions are incorporated into the coal structure by first contacting and soaking the coal with a solution comprising an alkali metal hydroxide at a temperature of about 20.degree. F. to 200.degree. F. to increase the concentration of ion-exchangeable sites within the coal structure. The coal is then further contacted with an alkaline earth metal compound at a temperature form about 20.degree. F. to about 200.degree. F. to replace a portion of the alkali metal cations with alkaline-earth metal cations.
Although processes available in the art have met with various degrees of commercial success, there still exist a need in the art for more economical and less complicated ways of dispersing organically bound cations, such as calcium, into the coal structure.